This invention relates to apparatus and methods for delivering aerosol particles, e.g. an aerosolized medicament, to the respiratory system of a subject through an invasive or noninvasive pressure-assisted breathing system. More specifically, one aspect of the invention is directed to apparatus and methods for delivering an aerosolized medicament from a nebulizer to a patient by a pressure-assisted breathing system.
The use of pressure-assisted breathing systems is well-known for the treatment of respiratory disorders and diseases in adults, e.g. infection, obstructive sleep apnea and respiratory insufficiency, and in children, e.g. abnormal breathing resulting from small or collapsible airways, small lung volumes, muscle weakness, respiratory distress syndrome, persistent obstruction following surgery, etc. As used herein, the term “pressure-assisted breathing system” means any artificial ventilation system that applies pressures, usually positive, to gas(es) in or about a patient's airway during inhalation as a means of augmenting movement of gases into the lungs. The term is intended to include mechanical ventilators and continuous positive airway pressure (“CPAP”) systems, which also includes bi-level positive airway pressure systems. The term is also intended to include both non-invasive and invasive systems. Systems that utilize an endotracheal or tracheostomy tube are examples of invasive pressure-assisted breathing systems. Systems that utilize nasal prongs or a mask are examples of non-invasive pressure-assisted breathing systems.
Pressure-assisted breathing systems utilize positive pressure during inhalation to increase and maintain lung volumes and to decrease the work of breathing by a patient. The positive pressure effectively dilates the airway and prevents its collapse. The delivery of positive airway pressure is accomplished through the use of a positive air flow source, e.g. a mechanical ventilator, that provides oxygen or a gas containing oxygen through a flexible tube connected to a patient interface device. The term “patient interface device” includes nasal prongs (cannula), nasopharyngeal tubes or prongs, an endotracheal tube, tracheostomy tube, mask, etc.
The tubes associated with commercially available pressure-assisted breathing systems create a “circuit” for gas flow by maintaining fluid communication between the elements of the circuit. Tubes can be made of a variety of materials, including but not limited to various plastics, metals and composites and can be rigid or flexible. Tubes can be attached to various elements of the circuit in a detachable mode or a fixed mode using a variety of connectors, adapters, junction devices, etc. These elements are sometimes collectively referred to herein as “junction devices”.
As an example of one such junction device, a mechanical ventilator system may utilize a ventilator circuit comprising an inspiratory tube that conducts a flow of gas from a ventilator and an expiratory tube that conducts a flow of gas back to the ventilator. This circuit (sometimes referred to herein as a “ventilator circuit”) is in fluid communication with a third tube (the “respiratory circuit”) that conducts a flow of gas to the patient interface device through a junction device, usually a tubular member in the shape of a “Y” or “T”. Such a junction device may comprise a first leg attachable to the inspiratory tube of the ventilator circuit, a second leg attachable to the expiratory tube of the ventilator circuit and a third leg attachable to the respiratory circuit. Other junction devices may be used, for example, to connect a nebulizer or a patient interface device to the appropriate circuit of the ventilator system.
Aerosol generators or nebulizers have been used to deliver an aerosol of medication through a ventilator system into the respiratory system of a patient. For example, U.S. Pat. No. 6,615,824, issued Sep. 9, 2003, and in co-pending U.S. patent application Ser. No. 10/465,023, filed Jun. 18, 2003, and Ser. No. 10/284,068, filed Oct. 30, 2002 describe apparatus and methods for connecting a nebulizer to a ventilator circuit to emit a aerosolized medicament directly into the flow of gas being delivered to a patient's respiratory system. As a result, the gas flows in circuits of ventilator systems are called upon to carry suspended aerosol particles from the aerosol generator to the patient.
It is imperative that a therapeutically effective amount of aerosolized medicament reach the desired sites in the patient's lungs to achieve a successful treatment, yet it is also desirable that the medicament be delivered in as efficient a manner as possible to minimize losses and waste. Although effective amounts of medicament delivered to a patient's airways in aerosol form, e.g. by the using a nebulizer connected to a ventilator system, are considerably less than the amounts needed to deliver a therapeutically effective amount of medicament systemically, current systems still exhibit inefficiencies. For example, aerosol particles being carried in the circuits of ventilator systems and other pressure-assisted breathing systems may be trapped on the inner walls of the tubes, deposited at irregular surfaces and obstructions in the tubes or other elements in the circuits, impact the interconnection between tubes of different diameters, or be diverted by sharply angled paths in the circuits. As one specific example, aerosol particles have to “turn corners” when traveling at relatively high flow rates through the sharply angled conduits presented by the “Y”, “T”, and “V”-shaped junction devices currently used in conventional pressure-assisted breathing system circuits. As a result, the aerosol particles may impact the walls of the junction device, and a portion of the particles may be diverted from the primary aerosol flow into various ports or branches in the circuits. As another example, aerosol particles may be deposited at the junction of a patient interface device and the respiratory tube connecting it to the ventilator circuit, or may be diverted or deposited within the patient interface device itself.
Accordingly, it is desirable to find ways to decrease the losses of aerosol particles within pressure-assisted breathing systems. In particular, increasing the efficiency in the delivery of aerosolized medicaments through ventilator systems, and the resulting smaller amounts of medicament required for a treatment, can represent a substantial advantage, particularly when scarce and expensive medicaments are employed.